Electromagnets and permanent magnets have been developed for moving magnet medical devices in the body. Some magnets used in medical applications apply a gradient to pull magnet medical devices within the body. Other magnets used in medical applications simply apply a magnetic field in a selected direction to align magnetic medical devices in the selected direction. Still other magnets apply both a magnetic field and a magnetic gradient to simultaneously orient and move a magnetic medical device.
There are a number of important competing design considerations for magnets used in medical procedures. First and foremost is providing sufficient field strength or gradient to orient or move the magnetic device. Electromagnets and in particular superconducting electromagnets can create strong magnet fields and gradients, but they are expensive to construct and operate. Until recently, it was difficult to construct a permanent magnet that could provide a sufficiently strong and universally directed magnetic field and gradient at a distance sufficiently far from the magnet to be useful in medical procedures. Recently, a focused permanent magnet has been developed which can create useful magnet fields at sufficient distances from the magnet to be employed in magnet surgery. The magnet is comprised of a plurality of segments each magnetized in a direction to contribute to the desired magnetic property, for example field strength at an operating point spaced in front of a magnet. This magnet and its method of design are disclosed in copending, co-owned, U.S. patent application Ser. No. 09/546,840, filed Apr. 11, 2000, U.S. patent application Ser. No. 09/497,467, filed Feb. 3, 2000, the disclosures of which are incorporated herein by reference. This magnet has other useful properties in that field direction could be changed by a simple translation of the magnet. However, these magnets still had relatively large exclusion zones to accommodate the movement of the magnet. The large exclusion zone made access to the patient, and positioning of other medical equipment (particularly imaging equipment) in the procedure room difficult. Thus a second design criteria is to minimize the exclusion zone, to provide greater access to the patient for medical staff and equipment.
A third design criteria is to minimize the degrees of freedom of magnet motion to provide a universally directed magnetic field. The fewer degrees of freedom of magnet motion needed, the simpler the navigation, and the less expensive the apparatus for moving the magnet.